FIG. 9 is a sectional view of conventional acoustic wave device 101, a chip-size packaged device. Acoustic wave device 101 includes piezoelectric substrate 102, interdigital transducer (IDT) electrode 103 provided on piezoelectric substrate 102, insulator 110 provided on piezoelectric substrate 102 for covering and protecting IDT electrode 103 from the outside.
Acoustic wave device 101 further includes internal electrode 104 provided on piezoelectric substrate 102, side wall 105 provided on internal electrode 104, lid 107 provided on side wall 105, electrode base layer 109 provided on internal electrode 104, and connection electrode 112 provided on electrode base layer 109.
Internal electrode 104 is made of, e.g. aluminum, and electrically connected to IDT electrode 103. Side wall 105 surrounds IDT electrode 103. Lid 107 is bonded to side wall 105 with adhesive layer 106 for covering space 108 provided above IDT electrode 103. Electrode base layer 109 is provided outside space 108 and side wall 105, and is made of, e.g. copper. Connection electrode 112 extends through insulator 110 for electrically connecting external electrode 111 to IDT electrode 103.
Connection electrode 112 has a columnar shape. Electrode base layer 109 is formed of metal thin film by a sputtering method. Then, connection electrode 12 is formed by an electrolytic plating method with electrode base layer 109 being energized.
In acoustic wave device 101, side wall 105 and internal electrode 104 may peeled off to produce a void between them. In this case, electrode base layer 109 is not attached strongly to the boundary between side wall 105 and internal electrode 104 when base layer 109 is formed by the sputtering. In such a case, internal electrode 104 is exposed from electrode base layer 109 at the boundary, so that plating solution used in foregoing electrolytic plating process corrodes internal electrode 104. As a result, internal electrode 104 may be broken, accordingly reducing a yield rate of acoustic wave device 101.